The chance has arrived, but not how he wanted it to go. He will be replacing an old friend on an interim basis in the middle of a season because of a serious illness.

The longtime NFL offensive coordinator has no illusions about the job as he tries to help the Colts get better while everyone hopes coach Chuck Pagano returns soon from leukemia treatments.

“This isn’t a head coaching job for me right now,” Arians said after being named Indianapolis’ interim coach Monday. “It’s just an expanded role as coordinator until Chuck comes back.”

Arians was an obvious choice.

The Colts’ front office followed Pagano’s advice and hired Arians, an assistant who had coached with or against Pagano for the better part of a decade.

He’s someone who mentored three quarterbacks selected No. 1 overall (Peyton Manning, Tim Couch and Andrew Luck) and has the same kind of personality that hooked the Colts on Pagano.

Team owner Jim Irsay and new general manager Ryan Grigson also liked his previous experience in Indianapolis and his résumé.

Arians played a key role in the development of Pittsburgh quarterback Ben Roethlisberger and won two Super Bowl rings with the Steelers – one as the receivers coach, the other as offensive coordinator – before his forced retirement earlier this year.

He spent two seasons as Paul “Bear” Bryant’s running backs coach at Alabama and six seasons as Temple’s head coach.

“He’s a veteran. He knows this game well. He has a great synergy with the staff and with Chuck,” Grigson said. “He’s going to be able to bridge that gap between Chuck and himself and this team because they (the assistants) have a brotherhood on that staff like I’ve never seen. … Bruce is the man to lead us forward while our leader is down.”

The plan in Indy is to let Arians call the shots temporarily. Players universally approve.

“Coach Arians and I spoke briefly about making sure the communication is not lost, so I don’t think it will be,” Luck said.

“He’s seen everything in the world of football, so I’m sure he’ll do a great job and still manage to keep his (finger on the) pulse of everything the offense is doing.”

Arians intends to keep calling plays, as he had planned to do if he ever got a head-coaching gig.

Indianapolis’ defense is embracing the choice, too.

How long Arians will be in charge isn’t clear. Pagano was admitted to an Indianapolis hospital last Wednesday to begin treatment.

Dr. Larry Cripe, Pagano’s physician, said the coach will be treated with chemotherapy and drugs – a process that usually requires patients to spend four to five weeks in the hospital.

Irsay said he expected Pagano to stay a bit longer, six to eight weeks, and does not anticipate Pagano taking over his full head-coaching duties the rest of this season.